In machine tools, the spindles of which rotate at a high speed, heat is generated in the roller bearings due to bearing friction, which heat is transmitted both onto the spindle and also onto the headstock. Due to an uneven temperature distribution in the bearing parts and the spindle, there results a shifting of the working or machining tools in direction of the spindle axis and radially of the axis of rotation of the tools, thereby rendering inexactnesses in the machining process. It is therefore common to forcedly cool the roller bearing outer rings by means of a cooling device. A cooling of the outer bearing rings, however, is not sufficient in view of the present demand for higher speed ranges and increasing requirements for precision. Only a very small portion of the heat which accumulates at the inner bearing rings can be discharged by a cooling of the outer bearing rings.
In order to also discharge heat from the inner bearing rings, a bearing sleeve which encloses the outer bearing rings is provided in a support for a machine tool spindle adapted for use with a cooling device of the above-mentioned type (German OS No. 19 57 974). The bearing sleeve has an axially parallel feed channel which, in the area of the roller bearings, is connected through crossbores to the inside of the roller bearings. The bearings sleeve has furthermore a discharge channel for the cooling medium which, near the spindle head, enters from the inside of the roller bearings into an annular chamber connected to the discharge channel. Lubricant oil is used as the cooling medium and is fed by means of a pump through the feed channel to the inside of the roller bearings. The lubricant oil in this manner reaches directly the inner bearing rings and also the outer bearing rings. The lubricant flows successively through the various roller bearings until it finally flows into the annular chamber, which is provided on the spindle head, and flows back from same through the discharge channel and an oil cooler into a storage container. This apparently simple solution is, however, in view of the cooling action little effective. That is, the roller members which rotate at a high speed create an oil foam which consists of oil and air, which oil foam is little suited for effecting a discharge of the heat. Furthermore, through the turbulence of the oil on the inside of the roller bearings heat is generated which in turn increase the amount of the accumulating heat. Since a satisfactory heat discharge cannot be assured in this known support, an additional correcting device is provided which controls the axial position of the spindle in response to its temperature. Such a correcting device, however, assumes that a bearing sleeve is axially movable in the headstock and furthermore complicated control devices are needed.
The basic purpose of the invention is to provide a machine tool spindle adapted for use with a cooling device in a headstock of the above-mentioned type, which is of a simple design and assures a satisfactory heat discharge from the inner bearing rings and thus secures a high operating speed and a simultaneous increase in the lifespan of the roller bearings.
This purpose is attained according to the invention by the feed and discharge channels being provided in the spindle and being connected with cooling grooves which, at least in the region of the inner bearing rings are arranged on the spindle head and extend in a peripheral direction or helically, are worked into the spindle outer surface and are open toward the inner bearing rings.
Through these relatively simple measures, a good lost heat discharge from the hub area of the inner bearing rings is assured. Since the cooling medium is guided through the cooling grooves to the inner bearing rings, it does not contact the roller members and, as a result, a foaming of the cooling medium is prevented, so that same can develop its full cooling action. Through a satisfactory heat discharge of the lost heat from the inner bearing rings, a heat transfer onto the spindle and its bearing parts is avoided and thus a high operating precision is also assured. Compared with supports adapted for use with a cooling device in which only the outer bearing rings are cooled, the inventive support also has a better cold-start behavior, because possible heat expansions do not need to be considered in measuring the bearing clearance. Finally, a good heat discharge from the inner bearing rings also leads to an increase in the life of the roller bearings.